The present invention relates to a method and an apparatus for controlling an internal combustion engine.
German Patent Application No. 197 49 814 discloses a method and an apparatus for controlling an internal combustion in which a first variable that characterizes the pressure in the combustion chamber of at least one cylinder is detected using a sensor.
There are other conventional devices with which the cylinder pressures of internal combustion engines can be measured over time or with respect to crank angle. Additionally, conventional methods have been described which allow a determination during operation, from a high-resolution pressure signal, parameters that are then in turn used for individual-cylinder optimization of the engine process in terms of fuel consumption, emissions, and comfort as target variables.
These applications are usually referred to as cylinder-pressure-based engine control systems. Conventional functions include closed-loop control of peak pressure, knock, combustion center point, combustion onset, and misfire recognition.
Parameters for this purpose are usually the latter""s absolute values or their relationships to specific points in time or angular positions, pressure differences with respect to the compression curve, pressure integrals and pressure-difference integrals, indicated work or indicated torque, or bandpass-filtered pressure curves integrated over an angle window.
It is provided, according to the present inventions, that in a method for controlling an internal combustion engine, at least a first variable that characterizes the pressure in the combustion chamber of at least one cylinder is detected using at least one sensor. On the basis of this first variable, a second variable is determined, the second variable characterizing the change in the first variable and/or the course of combustion. Open- and/or closed-loop control of operating parameters of the internal combustion engine is accomplished as a function of those two variables.
The first variable that is detected by means of a sensor may be the pressure in one or more of the combustion chambers. The second variable may be a variable derived from the first variable. It is particularly advantageous if the second variable characterizes the maximum value of the first variable and/or the maximum value of the change in the first variable and/or the position of the maximum values of the first variable. It is additionally advantageous if the second variable characterizes a heat curve, a combustion curve, a cumulative heat curve, a cumulative combustion curve (i.e., a net heat release rate, gross heat release rate, net heat release, gross heat release), a maximum value of and/or a maximum value of the change, a position of the maximum values of the heat curve, the combustion curve, the cumulative heat curve, and/or the cumulative combustion curve.
It is particularly advantageous if the gradient of the first variable is used as the second variable, i.e. if the second variable is definable on the basis of the derivative of the first variable.
A considerable gain in reliability is obtained if a control output is definable as a function of the comparison of the second variable to a threshold value. It is thereby possible to prevent the combustion chamber pressure from rising excessively, i.e. to avoid situations that might result in damage to the internal combustion engine.
It is also particularly advantageous if the boost pressure, the rail pressure, an air variable that characterizes the air quantity delivered to the internal combustion engine, and/or the duration and/or onset of at least one pre-injection, at least one main injection and/or at least one post-injection, is controlled in open- and/or closed-loop fashion as a function of the second variable.
According to the present invention, a variable that characterizes the course of combustion is determined, that variable is compared to a setpoint, and that the duration and/or onset of at least one pre-injection is definable on the basis of the comparison to the setpoint. This allows very accurate correction of the pre-injection during operation of the internal combustion engine.
In addition to the use of a combustion chamber pressure sensor, it is also advantageous to use a signal of a solid-borne sound sensor and/or of an ion current sensor, or a variable derived from those signals, for closed-loop control of the variable that characterizes the combustion process.